Roofing shingles are traditionally manufactured utilizing asphalt, which is derived from crude oil. Asphalt prices have recently increased even more rapidly than crude oil prices. In addition to the use and cost of crude oil in the asphalt manufacturing process, the process of manufacturing asphalt shingles further utilizes a considerable amount of fossil fuels heating both the asphalt and the fillers so that they can be combined. Typically, approximately 65% filler is mixed with approximately 35% asphalt. In order to create a mixture having a usable viscosity, the asphalt is heated to 450° F. while the filler is heated to approximately 350° F. prior to the two additives being mixed together.
Considerable waste is involved with the manufacture and use of asphalt roofing materials, such as shingles and roll roofing membranes. For example, each new asphalt roofing shingle has cutout tabs that are removed and discarded (this waste will be called “manufacturer's asphalt roofing shingle waste”) while old shingle materials removed from existing buildings (this waste will be called “post consumer asphalt shingle waste”) also adds to a significant amount of roofing material waste. In the US alone, 11 million tons of post consumer asphalt shingles are removed from roofs annually. Approximately 10 million of these tons are buried in landfills. Not only are landfill costs increasing, but access to landfills for recyclable products is becoming more restricted since roofing shingles are products which do not degrade. Asphalt shingles pose an additional particular problem to landfills because they restrict natural water movement causing delays with the natural decay of other items in the landfill. The asphalt shingles themselves do not degrade and stay permanently in the landfill.
Recycling of all types of roofing material waste has been discussed and attempted but has not been terribly successful. The waste generated from asphalt roofing materials presents a significant recycling as well as environmental concern because of the composition of the roofing material. Typical shingles are composed of a cellulose fiber saturated with asphalt or fiberglass mat, an asphalt coating on the mat, and granules disposed on the coating. Such materials are difficult to break down and have typically required complex recycling processes.
Past attempts at recycling asphalt shingles have failed to free up the asphalt into a usable form so that it can be successfully incorporated into commonly used asphalt based products, such as roof shingles and road pavement. If the granules in the recycled shingle material are not reduced to a fine powder, the granules will not remain suspended in an asphalt solution and the recycled shingle material cannot be reused in roofing or other products. Too fine of a granule also poses a problem in that the fine material does not have a significant use and is therefore not sellable.
In typical asphalt shingle construction, 42 percent of the weight is surfacing granules. The granules are usually made of trap rock which is colored by ceramic type process. The typical mesh size runs from 2 percent being retained on a 10 mesh screen to 2 percent retained on a 40 mesh screen. The sand backing accounts for 5 percent of the weight with the mesh running 2 percent retained on a 50 mesh and the rest smaller down to 25 to 35 mesh. The limestone filler runs from 2 percent retained on a 70 mesh to finer. Consequently, the hard minerals can be removed by passing the material through a screen having a mesh size between 35-50 mesh. The preferred mesh size is 36-38 mesh. If the granule or sand particles are broken, they could pass into the filled coating powder causing glass mat weakening related problems. 49 percent of the shingle weight is filler and asphalt or “filled coating”. The asphalt and filler are inseparable in this process with each particle of limestone completely coated with asphalt. The coarsest filler particles have 2 percent retained on a 70 mesh screen, but even though they are coated with asphalt they easily pass through 30-50 mesh screens. 5 percent of the shingle is sand. These sand particles fall within the limestone filler. While sand is a hard particle this small amount can be tolerated or removed using air separation, thereby exploiting the density difference between filled coating and sand. 2 percent of the shingle composition is the aforementioned glass mat. After processing, the fiber remains bound up with the asphalt/filler portion of the mix in the form of a “flake” and is screened out using a ¼ mesh screen. The remaining 2 percent consists of adhesives used to bond the shingles together.
Some past methods of recycling asphalt roofing material have used milling machines, such as rolling mills, bag mills, hammer mills, saw mills, etc. to produce a recycled roofing material which can be used only in road construction or as other similar “filler” material. However, merely milling the shingle material in a reduction mill without further processing has been unsuccessful in reducing the granules in the shingle material to a fine mesh so that the recycled asphalt can be reused in manufacturing new roofing products.
Asphalt roads are comprised of six percent paving grade asphalt and ninety-four percent aggregate. The particle size distribution is very specific and is carefully monitored by state and federal agencies. Prior attempts to use post factory and post consumer shingles have been stopped by four major issues. First, ⅜ inch chips (the standard currently in use) will not dissolve in the mixing process, so little asphalt is freed up for incorporation into the road (the entrained mix energy is lost) which causes the amount of asphalt and mineral to be inconsistent. Second, the plastic mylar on the back of all shingles is left as 4-5 inch by 1 inch pieces. Third, the nails may not be removed and fourth, the shingles contain too many fines. All of these issues create their own series of problems in recycling the materials for reuse in road asphalt blends. Nails cannot be present in the recycled material that is to be used, as nails in a road would pose serious problem. Likewise, the presence of fines in pavement asphalt creates air pockets and voids that affect the HMA performance in terms of rutting and cracking. Shingles contain 30-40 percent fines and the amount of fines needs to be reduced as low as possible because the fines increase viscosity causing more roller energy to be required (more passes over the pavement while hot) and they can have serious road quality implications. A new process is needed that resolves all of these issues.
One apparatus for recycling roofing shingles is disclosed in U.S. Pat. No. 4,706,893 to Brock. This apparatus includes a hammer mill that comminutes the shingles and a vessel that subsequently dries then mixes the recycled shingle material with liquid asphalt, for recycling as an asphalt paving composition. This milling process will not reduce the granules in the shingle material to a small enough size for the shingle material to be reused in applications other than an asphalt paving composition. Portions of the recycled material that are too fine are considered “fines”. Paving mix can only contain 2 percent fines or it becomes excessively viscous. This means that when it is pressed with a roller excessive voids may be created because compacting is difficult. Voids are mechanically weak areas, and they can cause premature failure due to having too much surface area exposed to oxygen. Asphalt becomes brittle with age due mostly to oxygenation. A ⅜ inch shingle chip or any combination of the full ingredients of a shingle contains 34 percent fines.
Another shingle reducing apparatus is disclosed in U.S. Pat. No. 5,385,426 to Omann. This complex apparatus includes a shredder, two hammer mills, and two heated vessels for drying the shingle material after it has been reduced. This apparatus further requires spraying the shingles with water prior to entering the first hammer mill in order to prevent sticking. The addition of water is a big problem in roofing manufacturing operations because vaporization increases water volume by 1600 percent, which can cause potential tank over flows and other unsafe conditions when mixed with hot asphalt. This extremely complex and involved process requiring two hammer mills also is not capable of completely reducing the granules in the recycled shingle material to a fine mesh or powder.
One reason milling machines have been unsuccessful in reducing the size of the granules in the recycled shingle material is because the shingle material was not heated as it was milled. In the past, heating the milling machine as the shingle material is milled was considered hazardous because of pressure build up in the closed milling vessel or heating vessel as a result of moisture in the shingle material. Heating would also make hammer mills gum up and not work because the asphalt would become sticky.
The typical recycling operation involves passing the material through a hammer mill to create ⅜ inch chips. Hammer mills function by revolving a pivot arm at a high speed and impinging the material between a plate and the hammer on the end of a pivot arm. The material is constrained in a chamber by a screen with holes of the desire output size. The impingement created breaks some of the surfacing granules into a fine powder and leaves the rest of the material in pieces the size of the screen holes (usually ⅜ inches). The only use for this material is in Hot Mix Asphalt for roads. This material cannot be used for asphalt roofing products because any hard minerals such as the surfacing granules or the sand used on the underside of the shingles (to prevent sticking in the bundles) cannot be used. Shingles are made by saturating and coating a fiberglass mat (13-15 mm diameter fibers, 1 to 1.5 inches long glued at fiber cross over junctions with a binder with a typical weight of 1.7 pounds per 100 square feet) with 65 percent limestone (a soft mineral) filler and 35 percent oxidized asphalt. This mixture is called “filled coating”. The surface is then covered with granules and the underside covered with sand. The hard minerals, granules and sand, cannot be present in quantity in the filler/asphalt mix because the coating process is roll over roll with the fiberglass mat passing through a nip. If excessive hard minerals are present, the pressure created within the nip causes breakage or abrading of the glass fibers. After exposure on the roof, the shingles would tear due to the weakened reinforcement. This problem caused widespread roof failures in the industry. At that time, rock dust was sometimes used as filler, so the same problem would occur if hard granules or sand were allowed into any fiberglass mat based roofing product.
Accordingly, what is needed is an asphalt shingle recycling system and method that is able to adequately process both new and post-consumer asphalt shingles into material of usable type and size as well as a material sorter which is able to sort the processed material into material of different sizes or grades for either more processing or for use in one or more applications. The process must remove all the offending hard minerals while capturing the filled coating.